// 合并两个有序数组
function merge(arr1, m, arr2, n) {
    let l1 = m - 1
    let l2 = n - 1
    let l = m + n - 1;
    while (l2 > 0) {
        // 边界问题
        if (l1) {
            arr1[l--] = arr2[l2--]
            continue
        }
        arr1[l--] = arr1[l1] > arr2 ? arr1[l1--] : arr2[l2--]
    }
}
